Chemical Composition of the Essential Oil From Minthostachys acris Schmidt-Leb. Grown in the Peruvian Andes

Abstract

The chemical composition of the essential oil from aerial parts of Minthostachys acris Schmidt-Leb. grown in Cuzco was studied. A total of 59 volatile compounds were identified by gas-chromatography-flame ionization detector and gas chromatography-mass spectrometry in the essential oil obtained by steam distillation, of which the most prominent were pulegone (54.4%), cis-menthone (11.0%), and thymol (6.3%).

The genus Minthostachys Griseb. (Lamiaceae) is found in middle elevations along the Andes, from Venezuela to Argentina. ¹ This genus includes 17 species according to some authors. ² The review of the literature shows that much research has been directed at Minthostachys verticillata and Minthostachys mollis that at any other species. ² In particular, Minthostachys acris Schmidt-Leb. is an aromatic shrub, growing wild in the Cuzco area and used as seasoning, for treatment of diarrhea, colics, flatulence, stomach pain, bruises, and for pest protection of stored tubers. ² Minthostachys acris is frequently treated as separate in Peruvian researches, but then erroneously called Minthostachys glabrescens (Benth.) Epling. ² The unique report about the chemical composition of M. glabrescens essential oil found pulegone, menthone (or trans-menthone), and isomenthone (or cis-menthone) as the major components. ³ Therefore, the present study was done to analyze the chemical composition of the essential oil from aerial parts of M. acris Schmidt-Leb. grown in Cuzco.

A total of 59 volatile compounds were identified in the essential oil (99.8% of the total composition) (Table 1). A chemical study on the volatile oil from leaves of Peruvian M. acris species have been carried out, with the presence of 36 compounds, in which the main components were pulegone (45.3%), trans-menthone (17.8%), and cis-menthone (6.4%). ³ Results of this work showed a different pattern compared to those previously found, particularly that the trans-menthone/cis-menthone ratio is opposed. Information available on the essential oil composition for other Minthostachys species showed that M. mollis var. mandoniana (Briq.) Schmidt-Leb. from Bolivia contained high amounts of pulegone and menthone ⁴ and M. verticillata (Griseb.) Epling from Argentina was pulegone dominated. ⁵ Many studies show that the chemical composition of essential oils varies noticeably according to numerous factors, including environmental geobotanical conditions, cultivation technique, plant age, harvest period, among others. ⁶

Table 1

Chemical Composition of Minthostachys acris Essential Oil.

Compound	LRIA	LRIP	%
Methyl 2-methylbutanoate	772	1011	tr
(E)-2-Hexenal	857	1232	tr
α-Thujene	932	1020	tr
α-Pinene	939	1032	0.2
3-Methylcyclohexanone*	951	1335	0.1
β-Pinene	976	1114	2.3
1-Octen-3-ol	982	1451	tr
p-3-Menthene*	986	-	tr
Myrcene	991	1162	0.1
Octan-3-ol	993	1386	tr
α-Phellandrene	1003	1160	0.2
α-Terpinene	1016	1179	0.5
p-Cymene	1025	1270	2.0
Limonene	1028	1202	1.0
1,8-Cineole	1031	1215	1.3
(Z)-β-Ocimene	1037	1244	0.2
(E)-β-Ocimene	1051	1250	0.1
γ-Terpinene	1063	1244	0.9
Terpinolene	1090	1278	0.1
Linalool	1096	1354	1.4
2-Methylbutyl 2-methylbutanoate	1098	1286	0.1
3-Methylbutyl 2-methylbutanoate	1100	1273	tr
1-Octen-3-yl acetate	1115	1381	0.4
3-Octyl acetate	1124	1345	tr
allo-Ocimene*	1132	1384	tr
trans-Menthone	1151	1474	1.6
Menthofuran*	1160	1483	tr
cis-Menthone	1163	1503	11.0
trans-Isopulegone	1175	1597	3.6
Terpinen-4-ol	1177	1590	tr
α-Terpineol	1189	1698	0.1
Verbenone	1205	1733	tr
Linalyl formate	1218	1570	0.3
Pulegone	1237	1665	54.4
Piperitone	1254	1743	0.1
(E)-Anethole	1284	1845	tr
Thymol	1290	2167	6.3
Carvacrol	1299	2236	0.3
α-Terpinyl acetate	1350	1706	0.9
α-Gurjunene	1409	-	tr
β-Caryophyllene	1419	1604	3.1
β-Ylangene	1423	1587	0.1
Aromadendrene	1441	1640	0.3
α-Humulene	1453	1664	0.3
allo-Aromadendrene	1460	1660	0.3
cis-Muurola-4(14),5-diene*	1467	-	tr
trans-Cadina-1(6),4-diene*	1476	-	0.2
γ-Muurolene	1480	1680	0.2
2-Phenylethyl 3-methylbutanoate	1488	1992	tr
(Z,E)-α-Farnesene*	1491	1737	0.1
δ-Selinene	1493	1707	0.5
Viridiflorene	1497	1710	1.2
α-Muurolene	1500	1734	tr
Bicyclogermacrene	1503	1756	1.2
γ-Cadinene	1514	1775	0.6
δ-Cadinene	1524	1748	2.0
trans-Cadina-1(2),4-diene*	1533	-	0.1
α-Cadinene	1539	1813	0.2

LRI_A and LRI_P experimental linear retention indices on DB-5ms and HP-Innowax columns, trace (<0.1%). *tentatively identified compound by comparison with literature data.

Experimental

Materials and Isolation of Essential Oil

Leaves were collected in Julio 2011 from wild shrubs in the Cuzco region in southeast Peru (2941 m height above sea level). Voucher specimen (accession numbers 763 CUZ) was deposited at the herbarium of the National University of San Antonio Abad del Cusco. The sample (10 kg) from different plants was steam distilled in a metallic distillation apparatus coupled to a Clevenger-type collector. Oil yield was 0.21 % v/m.

Gas Chromatography

Analyses of the essential oil was performed by gas chromatography with a flame ionization detector (GC-FID) on a Konik 4000A (Konik, Barcelona) coupled to a 30 m × 0.25 mm di ×0.25 µm HP-5ms or HP-Innowax column under the experimental conditions: 60°C (2 min), 60°C to 220°C (4°C/min) and 220°C (5 min); helium flow rate at 1 mL/minutes; injector and detector temperature 240°C.

For GC-MS an Agilent 6890N (Santa Clara, CA, EE.UU.) coupled to a mass detector Agilent 5975B was used. The column and analytical conditions were the same as GC-FID. Compounds were identified using their linear retention indices and mass spectra. Linear retention indices, calculated using linear interpolation relative to retention times of C₈-C₂₄ of n-alkanes, were compared with those standards and data from the literature. ⁷ Mass spectra were compared with corresponding reference standard data ⁷ and mass spectra from NIST 05, Wiley 6, NBS 75 k and in-house Flavorlib libraries.